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Tidy up macro_rules grammar.

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This commit is contained in:
Graydon Hoare 2012-10-10 17:08:10 -07:00
parent 58807b0500
commit c639f44adb
1 changed files with 8 additions and 6 deletions
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14
doc/rust.md
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@ -478,11 +478,8 @@ with values. `proto!` is an item, defining a new name.
## Macros
User-defined syntax extensions are called "macros", and they can be defined
with the `macro_rules!` syntax extension. User-defined macros can currently
only be invoked in expression position.
~~~~~~~~ {.ebnf .gram}
~~~~ {.ebnf .gram}
expr_macro_rules : "macro_rules" '!' ident '(' macro_rule * ')'
macro_rule : '(' matcher * ')' "=>" '(' transcriber * ')' ';'
matcher : '(' matcher * ')' | '[' matcher * ']'
@ -494,13 +491,18 @@ transcriber : '(' transcriber * ')' | '[' transcriber * ']'
| '$' '(' transcriber * ')' sep_token? [ '*' | '+' ]
| non_special_token
~~~~
~~~~~~~~
User-defined syntax extensions are called "macros", and they can be defined
with the `macro_rules!` syntax extension. User-defined macros can currently
only be invoked in expression position.
(A `sep_token` is any token other than `*` and `+`. A `non_special_token` is
any token other than a delimiter or `$`.)
Macro invocations are looked up by name, and each macro rule is tried in turn;
the first successful match is transcribed. The matching and transcribing
processes are close cousins, and will be described together:
processes are closely related, and will be described together:
### Macro By Example